1. Field of the Invention
The present invention relates to a magnetic head having a CPP (Current Perpendicular to the Plane) structure in which a sensing current is applied in a direction substantially perpendicular to the interface between the first ferromagnetic layer and the intermediate layer of a magnetoresistive film and the interface between the intermediate layer and the second ferromagnetic layer of the film and to a magnetic recording/reproducing system having the magnetic head.
2. Description of the Related Art
Surprisingly, the recording density of a magnetic recording/reproducing system has been increasing at an annual rate of 100%. Along with this, a magnetic head mounted to a magnetic recording/reproducing system is required to have higher output and a narrower shield to shield distance.
To achieve higher output, attempts have been made to improve the performance of a magnetoresistive film. An anisotropic magnetoresistive (AMR) film has been used to achieve a recording density up to several Gb/in2 but a giant magnetoresistive (GMR) film capable of obtaining high output is now used to achieve a recording density higher than the above value.
Further, a tunnel magnetoresistive (TMR) film as disclosed in Journal of Magnetism and Magnetic Materials, vol. 139, pp. L231 to L234 published in 1995 and a CPP (Current Perpendicular to the Plane)-GMR film in which a current is applied in a direction perpendicular to the plane of a GMR film as disclosed in Journal of Applied Physics, vol. 89, pp. 6943 to 6945 published in 2001 are under research and development as next-generation magnetoresistive films after the GMR film.
To achieve a narrower shield to shield distance, in the case of a so-called CIP (Current Into the Plane) GMR film in which a sensing current is applied to the plane of a magnetoresistive film, as the thickness of an insulating gap layer interposed between shield layers and the GMR film and between shield layers and electrode films for supplying a sensing current to the GMR film become small and a sensing current leaks out into the shield layer, when the shield to shield distance is set to about 80 nm or less, the yield greatly lowers, and it is technically difficult to reduce the shield to shield distance to 70 nm or less. Since an insulating gap film as seen in a CIP structure becomes unnecessary in a CPP structure in which a sensing current is applied in a direction perpendicular to the plane of the magnetoresistive film, it can be said that the CPP structure is advantageous in reducing the shield to shield distance.
Since the CPP structure is a new structure unlike the CIP structure whose technology is becoming mature, it still has some problems to be solved. One of the problems is a air bearing surface processing technology. As for a magnetic head comprising a TMR film as a magnetoresistive film having a CPP structure, JP-A 11-175927 discloses a method employing a plasma process for air bearing surface processing, and JP-A 2001-28108 discloses a technology for carrying out air bearing surface processing after ferromagnetic layers below and above the barrier layer of a TMR film are short-circuited. JP-A 11-175920 and JP-A 2000-215415 disclose a layer underlying the ferromagnetic film or antiferromagnetic film of a TMR film and the material of a lower electrode layer.
In order to improve the yield of air bearing surface processing, JP-A 2002-133614 discloses a GMR head having a double shield layer structure consisting of an inner layer and an outer layer formed in the order named from a magnetoresistive film, the inner layer having higher hardness than the outer layer.
The above prior arts disclose air bearing surface processing technologies when the magnetoresistive film is a TMR film. JP-A 11-175927 aimed to improve deteriorated magnetoresistive properties caused by a damaged layer by processing formed by air bearing surface processing, particularly a damaged layer by processing for a barrier layer, and JP-A 2001-28108 aimed to reduce a damage in the wafer process and air bearing surface process.
However, the step of obtaining a desired sensor height using the plasma process disclosed by JP-A 11-175927 in air bearing surface processing has a poor throughput, is not practical and needs mechanical polishing. Even in the structure for short-circuiting the ferromagnetic layers above and below the barrier layer disclosed by JP-A 2001-28108, a short-circuit can be maintained in the rough process before a predetermined sensor height is obtained but a short-circuited portion is removed in the precision process in which a predetermined sensor height is obtained.
JP-A 11-175920 names 23 metals including Ti, V and Cu for use in the underlayer of the ferromagnetic film or anti-ferromagnetic film, and JP-A 2000-215415 names 12 metals including Ta, Zr and Au as materials for the lower electrode layer. Since soft and deformable materials such as Cu and Au are selected, it can be assumed that a damage by mechanical polishing at the time of air bearing surface processing is not taken into account.
JP-A 2002-133614 includes a description of a shield layer structure which is hardly deformed for a CIP structure GMR head. Since a GMR film which is a magnetoresistive film is sandwiched between insulating gap layers made from a material which is hardly deformed such as alumina in the case of a GMR head, the deformation of the GMR film itself hardly occurs. Therefore, the main cause of deteriorating properties during air bearing surface processing is the shield layer. More specifically, when a air bearing surface is to be polished, a metal constituting the shield layer is dragged from the insulating gap film to the GMR film, thereby causing a phenomenon that a sensing current leaks out from the GMR film into the shield layer to greatly reduce output. This problem can be solved by making only the shield layer from a material having high hardness.
However, as the magnetoresistive film, the gap layer and the shield layer are made from a metal in the CPP structure head, all of them are readily deformed, whereby the dragging of a metal constituting the shield layer which occurs in the CIP structure head occurs, and also the deterioration of characteristics is caused by the deformation of the gap layer and the deformation of the magnetoresistive film (disorder and fault of the laminate structure). Therefore, in the case of the CPP structure head, taking the mechanical properties of only the shield layer into consideration is unsatisfactory, and it is important that the magnetoresistive film, the gap layer and the shield layer should be entirely made difficult to be deformed. Since shearing stress is applied at the time of air bearing surface processing, the mechanical property that must be taken into consideration is shear modulus. The shear modulus of a material disclosed by JP-A 2002-133614 is 7.1 to 8.3×1010 Pa according to calculation by the inventor of the present invention.